Cannot bootstrap for PowerPC with LLVM assertions enabled

[alexcrichton]

Relevant code to disable this

From these logs.

rustc: x86_64-unknown-linux-gnu/stage2/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore
rustc: x86_64-unknown-linux-gnu/stage2/lib/rustlib/aarch64-unknown-linux-gnu/lib/libcore
rustc: x86_64-unknown-linux-gnu/stage2/lib/rustlib/arm-unknown-linux-gnueabi/lib/libcore
rustc: x86_64-unknown-linux-gnu/stage2/lib/rustlib/arm-unknown-linux-gnueabihf/lib/libcore
rustc: x86_64-unknown-linux-gnu/stage2/lib/rustlib/armv7-unknown-linux-gnueabihf/lib/libcore
rustc: x86_64-unknown-linux-gnu/stage2/lib/rustlib/mips-unknown-linux-gnu/lib/libcore
rustc: x86_64-unknown-linux-gnu/stage2/lib/rustlib/mips-unknown-linux-musl/lib/libcore
rustc: x86_64-unknown-linux-gnu/stage2/lib/rustlib/mipsel-unknown-linux-gnu/lib/libcore
rustc: x86_64-unknown-linux-gnu/stage2/lib/rustlib/mipsel-unknown-linux-musl/lib/libcore
rustc: x86_64-unknown-linux-gnu/stage2/lib/rustlib/powerpc-unknown-linux-gnu/lib/libcore
rustc: x86_64-unknown-linux-gnu/stage2/lib/rustlib/powerpc64-unknown-linux-gnu/lib/libcore
Invalid PPC CTR loop!
UNREACHABLE executed at /buildslave/rust-buildbot/slave/auto-linux-cross-opt/build/src/llvm/lib/Target/PowerPC/PPCCTRLoops.cpp:722!
Aborted (core dumped)
make: *** [x86_64-unknown-linux-gnu/stage2/lib/rustlib/powerpc-unknown-linux-gnu/lib/stamp.core] Error 134

This means we do not blanket turn on LLVM assertions on all of our bots, which we would ideally like to do. I'm going to try turning them off for just the cross bot though.

[alexcrichton]

cc rust-lang-deprecated/rust-buildbot@571864e

cc @eddyb

[nagisa]

Seems related to https://llvm.org/bugs/show_bug.cgi?id=27083 somewhat. We do not use the maxnum intrinsic (totally should!) but from the existence of bug for maxnum seems to suggest that a similar issue for some non-maxnum intrinsic is likely to exist (and libcore is kinda intrinsic-heavy).